Background: Fluoxetine is an inhibitor of the main metabolizing enzymes of lansoprazole and could influence the pharmacokinetics of lansoprazole. The changes in lansoprazole pharmacokinetics could have clinical significance concerning the safety of the therapy.
Objective: The aim of this study was to evaluate the pharmacokinetic interaction between fluoxetine and lansoprazole in healthy subjects.
Methods: A dose of lansoprazole 30 mg, alone or in combination with fluoxetine 60 mg, was administered to 18 healthy male subjects in a two-treatment study design, separated by an 8-day period in which fluoxetine alone was administered as a single oral daily dose. Plasma concentrations of lansoprazole were determined during a 12-hour period following drug administration. Lansoprazole plasma concentrations were determined by a validated liquid chromatography-mass spectrometry method. The pharmacokinetic parameters of lansoprazole were calculated using non-compartmental analysis.
Results: In the two periods of treatment, the mean maximum plasma concentration (C(max)) values were 817 ng/mL (lansoprazole alone) and 1370 ng/mL (lansoprazole in combination with fluoxetine after pre-treatment with fluoxetine for 8 days) [p < 0.0001]. The observed area under the plasma concentration-time curve (AUC) from time zero to time of last measurable concentration values were 2400 and 6220 ng · h/mL (p < 0.0001), respectively, and the AUC from time zero to infinity values were 2480 and 7290 ng · h/mL (p < 0.0001), respectively. The time to reach C(max) values were 2.72 and 2.64 hours, respectively. The elimination rate constant from the central compartment values were 0.50 and 0.21 h-1, respectively (p < 0.0001). The elimination half-life values were 1.47 and 3.56 hours (p < 0.0001), respectively, and the mean residence times were 4.0 and 6.9 hours (p < 0.0001), respectively.
Conclusion: The data demonstrate a pharmacokinetic interaction between fluoxetine and lansoprazole and suggest that the observed interaction may be clinically significant, although its clinical relevance has yet to be confirmed.